To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. The wide-spreading flash memory market and the demand for increased storage capacities drive forward the miniaturization technology. As the advanced miniaturization technology, the double patterning version of ArF lithography is implemented to manufacture devices of 10 nm order on a mass scale.
The lithography of next generation to the ArF lithography is EUV lithography of wavelength 13.5 nm. For mask writing, the EB lithography is used in the art.
With respect to high-energy radiation of very short wavelength such as EB or EUV, hydrocarbons and similar light elements used in resist materials have little absorption. Then polyhydroxystyrene base resist materials are under consideration.
The exposure system for mask manufacturing made a transition from the laser beam exposure system to the EB exposure system to increase the accuracy of line width. Since a further size reduction became possible by increasing the accelerating voltage of the electron gun in the EB exposure system, the accelerating voltage increased from 10 kV to 30 kV and reached 50 kV in the current mainstream system, with a voltage of 100 kV being under investigation.
As the accelerating voltage increases, a lowering of sensitivity of resist film becomes of concern. As the accelerating voltage increases, the influence of forward scattering in a resist film becomes so reduced that the contrast of electron image writing energy is improved to ameliorate resolution and dimensional control whereas electrons can pass straightforward through the resist film so that the resist film becomes less sensitive. Since the mask exposure tool is designed for exposure by direct continuous writing, a lowering of sensitivity of resist film leads to an undesirably reduced throughput. Due to a need for higher sensitivity, chemically amplified resist compositions are studied.
As the feature size reduces, image blurs due to acid diffusion become a problem. To insure resolution for fine patterns with a size of 45 nm et seq., not only an improvement in dissolution contrast is important as previously reported, but control of acid diffusion is also important as reported in SPIE Vol. 6520 65203L-1 (2007). Since chemically amplified resist compositions are designed such that sensitivity and contrast are enhanced by acid diffusion, an attempt to minimize acid diffusion by reducing the temperature and/or time of post-exposure bake (PEB) fails, resulting in drastic reductions of sensitivity and contrast.
A triangular tradeoff relationship among sensitivity, resolution, and edge roughness has been pointed out. Specifically, a resolution improvement requires to suppress acid diffusion whereas a short acid diffusion distance leads to a loss of sensitivity.
The addition of an acid generator capable of generating a bulky acid is an effective means for suppressing acid diffusion. It was then proposed to incorporate in a polymer an acid generator of an onium salt having a polymerizable olefin. JP-A 2006-045311 discloses a sulfonium salt having polymerizable olefin capable of generating a specific sulfonic acid and a similar iodonium salt. JP-A 2006-178317 discloses a sulfonium salt having sulfonic acid directly attached to the backbone.
In the EUV lithography, a tradeoff relationship between sensitivity and edge roughness has been pointed out. For example, SPIE Vol. 3331 p 531 (1998) describes that sensitivity is in inverse proportion to edge roughness. It is expected that the edge roughness of a resist film is reduced by increasing the exposure dose to reduce shot noise. SPIE Vol. 5374 p 74 (2004) describes a tradeoff between sensitivity and roughness in the EUV lithography in that a resist material containing a more amount of quencher is effective in reducing roughness, but suffers from a decline of sensitivity at the same time. This suggests a need for a new resist material capable of solving the problem.
As the acid generator which can be blended to suppress acid diffusion, an acid generator adapted to generate an acid of giant molecular weight is proposed. For example, there are proposed acid generators capable of generating fluorosulfonic acid having steroid skeleton, acid generators capable of generating fluorinated tetraphenyl borate, and acid generators capable of generating sulfonic acid having rings linked by a plurality of linking groups. See Patent Documents 3 to 6.